Posed a question this past week about soundproofing a bathroom. Now, how about soundproofing my 1st floor ceiling? The bedrooms and bathroom are on the second floor... above the living room, dining room, kitchen, office, etc. Am going to insulate below the 2nd floor bathroom for sure and am considering insulating elsewhere as well if time and money permits. I have 9 1/2" deep floor joists. Should I use 4" batts up tight agains the bottom of the floor, 6" batts, or thicker? I'd like to just use the 4" batts for $$$ reasons as this wasn't planned in the budget, but would conside 6's or 8's if that much better and not significantly more cost. Note - I'm not going to use resilient channels or double layers of drywall or anything like that... not enough time nor $$ for such measures. Thanks.